Emission Features

  • Emission Features

Resonance Scan

  • Identification of resonant structures and their resonant frequencies
  • Single probe for measuring DUT responses to external noise

Resonances increase coupling from electromagnetic fields to circuits, which can reduce immunity and amplify system emissions. Resonances often act as “missing links” between system-level performance and local-level behavior. Therefore, identifying resonances is a critical step in understanding immunity sensitivity and the maximum emission levels of a system.

Two orthogonal (or decoupled) probes are used to measure S21. If a resonant structure is present, the S21 value will be high; otherwise, it will remain low.

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<Figure: Test structure overlaid with resonance scan results>

Use Cases (For Both Emission and Immunity)

For EMI Scan

First, a resonance scan is performed with the DUT powered OFF. This identifies the resonant structures’ frequencies, locations, and Q-factors.
In the second step, the DUT is powered ON and an EMI scan is conducted to determine which structures exhibit emissions at specific frequencies. EMI engineers understand that resonant structures can act as much stronger antennas than non-resonant structures.
In the third step, the results of both scans are compared to identify which frequency components occur in the resonant structures. If a frequency component is present in a resonant structure, it can reasonably be concluded that the structure strongly contributes to the emission.

For Immunity Scan

The challenge with RF sine-wave immunity scans is that each test point’s frequency sweep can be time-consuming, making it impractical to test every frequency at every point. Therefore, the number of test points and frequencies must be carefully limited. Resonance scanning helps resolve this dilemma.
First, a resonance scan is performed with the DUT powered OFF, identifying the resonant frequencies, locations, and Q-factors of potential structures. In the second step, the DUT is powered ON and monitored for disruptions. The probe then applies RF signals—such as modulated signals via field coupling—only at the locations and frequencies where resonances have been detected. This is because external fields, as used in standard immunity tests, couple most efficiently to resonant structures. By focusing the test in this way, the overall duration of the RF sine-wave immunity scan can be significantly reduced.

Required Equipment

  • SmartScan-RS (software)
  • VNA (Vector Network Analyzer) or spectrum analyzer
  • Resonance probe
Note on resonance probe:
The probe is a critical element of the resonance scan, measuring how the DUT responds. The excitation and response fields must be decoupled to ensure accurate results.

Please also see our Rohde & Schwarz products

Rohde & Schwarz products

Emission Features

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